A normal ear directs sounds as shown in FIG. 1 from the outer ear pinna 101 through the generally cylindrical ear canal 110 to vibrate the tympanic membrane 102 (eardrum). The tympanic membrane 102 moves the bones of the middle ear 103 that vibrate the cochlea 104, which in turn functions as a transducer to generate electric pulses to the brain that are interpreted as sounds. In addition, the inner ear also includes a balance sensing vestibular system which involves the vestibular labyrinth 105, its three interconnected and mutually orthogonal semi-circular canals: the superior canal 106, posterior canal 107, and horizontal canal 108 (as well as the otolith organs, the utricle and saccule—not shown). The canals and spaces of the vestibular labyrinth 105 are filled with endolymph fluid which moves relative to head movements, thereby activating hair cells that send an electrical balance signal to the brain via the vestibular nerve 111.
In some people, the vestibular system is damaged or impaired, causing balance problems such as unsteadiness, vertigo and unsteady vision. Vestibular implants are currently under development, with one of the challenges being to stimulate the fibers of the vestibular nerve 111, which lie embedded in a plane in a bony channel surrounding the vestibular labyrinth 105. These nerve fibers need to be stimulated at several different specific locations, suggesting use of a multi channel electrode.
The electrode contacts of such a multi channel electrode need to be as close as possible to the nerve fiber, but yet still some distance away, for example, a few microns up to some tens of microns away from the nerve fibers. To surgically approach the nerve fibers, some of the surrounding bone may be drilled away until a membranous periosteum is exposed, thereby creating an electrode well just above the plane of the nerve fibers. The electrode well may be conical in shape due to the spherical drill burr, 100 microns to 1 mm or more in depth. Or the electrode well may be extended in some lateral direction creating a shoe box-shape well.
Once an electrode well has been surgically prepared, a multi channel electrode with a collection of electrode contacts needs to be placed in it. A planar shape electrode could be used, but it would need to be extremely flexible and yet robust enough to adapt to the shape of the electrode well. And the connection between the electrode contacts and the bottom of the electrode well may be less than optimum with a planar electrode. The placement of a planar electrode in the electrode well also may be hindered by the electrode lead that connects the electrode contacts to the implanted stimulator device.